1. Field of the Invention
The present invention relates to a fixing device and an image forming device provided with the fixing device.
2. Description of Related Art
An image forming device such as a laser printer is usually provided with a fixing device that has a heat roller and a pressure roller, and a toner image that has been transferred onto paper is thermally fixed as the paper passes between the heat roller and. the pressure roller.
To prevent the paper from rolling around the heat roller in such a fixing device, it is known to provide a plurality of separation claws at positions along the axial direction of the heat roller. The plurality of separation claws are disposed on the side that is further downstream in the rotational direction of the heat roller from the contact portion between the heat roller and the pressure roller, so that the paper is separated from the heat roller by the separation claws after the fixing.
As disclosed in Japanese patent-application publication (kokai) No. HEI-2-208679, it is also known to provide a separation guide having a very small space from a rotational body for fixing (that is, a heat roller) within an image area and to bring the separation guide into contact with the rotational body outside the maximum image area so that the paper is separated from the rotational body by the separation guide.
In such a fixing device, a halogen heater is provided within the heat roller and a thermistor is provided in the neighborhood of the surface of the heat roller. The fixing temperature of the heat roller is set by controlling the halogen heater based on the temperature detected by the thermistor.
The thermistor is provided further downstream in the rotational direction of the heat roller and does not normally come into contact with the paper. However, if the paper is not peeled off or separated from the heat roller by the separation claws, it is possible that the paper will be conveyed onward until the paper comes into contact with the thermistor and the thermistor could be deformed thereby.
For that reason, Japanese patent-application publication (kokai) No. 2000-98775 proposes to provide deformation prevention members in the heat roller at portions corresponding to the thermistor on the upstream and downstream sides in the rotational direction, to prevent deformation of the thermistor by guiding the paper that has not been separated from the heat roller along the heat roller by the deformation prevention member.